Communication system using multiple wireless resources during a soft handoff

ABSTRACT

In a wireless communications system operating according to CDMA or the like, when one terminal simultaneously performs communication using multiple wireless resources (e.g., multiple carriers), there was a problem that when it was attempted to guarantee network mobility by the same soft handoff system as in the case where communication was performed using only one wireless resource, efficiency suffered from the viewpoint of network forwarding load, processing load and wireless resource occupancy time. Soft handoff termination is judged and soft handoff is forcibly terminated according to whether or not the data rate obtained for all resources on the network side satisfies a requested rate, based on a reception state notification from a terminal concerning wireless resources. By performing this processing, the soft handoff period is shortened, sufficient received strength in the terminal is maintained and terminal mobility is guaranteed, while at the same time network forwarding load, terminal processing load and wireless resource occupancy time are suppressed to the absolute minimum.

CLAIM OF PRIORITY

This application is a Divisional of U.S. Ser. No. 11/822,228 filed Jul.3, 2007. Priority is claimed based on U.S. Ser. No. 11/822,228 filedJul. 3, 2007, which claims priority to Japanese Patent Application fromJapanese application JP 2006-234897 filed on Aug. 31, 2006, the contentof which is hereby incorporated by reference into this application.

FIELD OF THE INVENTION

The present invention is suitable for wireless communications systemsterminals and base stations that support terminal mobility such asmobile phones and wireless LAN, and particularly, for those usingMC-CDMA (multi carrier code division multiple access).

BACKGROUND OF THE INVENTION

Wireless communications systems such as mobile phones aim to enablecommunication “anytime and anywhere” without interruption, and havedeveloped to support the expansion of communication areas and handofftechnology between base stations.

Recently, the data amount being exchanged by a single user has beenrapidly increasing, such as E-mails with photographic or moving imagefiles attached, and motion picture of Video phones for example. Wirelesscommunication systems are required to enable further enhancement ofmaximum data throughput.

Also, new wireless communications systems with lower terminal mobilitybut higher data throughput (close to cable network level), such asWireless LAN or WiMAX and the like, are now appearing. Thus, there is apressing need to achieve balanced mobility and higher data throughputfor future mobile phone systems.

SUMMARY OF THE INVENTION

In order to obtain higher data throughput, whereas communication withthe base station was previously made through only one carrier frequency,it is now being considered to increase the communications throughput Ntimes by permitting communication via multiple carriers for 1 usersimultaneously. For instance, 1×EVDO method of 3GPP2 (3GPP2C.S0024-A_v2.0 (8.7.6.1.6.3, Active Set Maintenance)) is a communicationstandard for the Code-Division Multiple Access system that uses onecarrier. If you try to enhance the communication capability for eachterminal N times by using N carriers with the conventional soft handoffmethod, the efficiency and the stability will become problems. In thefollowing, these problems are described in detail.

To resolve this issue, it is necessary to understand the basic method ofthe soft handoff. Method to guarantee terminal mobility in the case ofusing one carrier will be discussed first.

In conventional 1×EVDO system, terminal mobility is guaranteed by usinga method called soft handoff between base stations, wherebycommunication is not interrupted even if the terminal moves to acommunication area of another base station adjacent to the firstcommunication area. In soft handoff, multiple base stations in adjacentcommunication areas cooperate, and a series of downlink transmissiondata is distributed to one terminal alternately from multiple basestations. Although the received strength of the pilot signal from eachbase station in the terminal changes momentarily due to fading ormovement of the terminal, the base station with the best receivedcondition is selected from among multiple candidates so that data isalways sent under good received conditions (without breaking off thecommunication). Details of the soft handoff method will now be describedusing 3GPP2 C.S0024-A_v2.0 (8.7.6.1.6.3—Active Set Maintenance) and FIG.4. In FIG. 4, the procedure when soft handoff is performed, is shownsequentially.

Sequence (401)

The terminal and base station manage a list of near-by base stations,called an Active Set of that terminal, having the downlink (basestation→terminal) pilot signal received strength greater than athreshold. The Active Set is managed by the terminal beforecommunication starts, and by a controller (ANC) connected on the basestation side of the network after communication starts. When the pilotsignal received strength from another new base station (ANTS-B) isdetected higher than a threshold while communicating with a certain basestation (ANTS-A), the terminal (AT) transmits a Route Update message(401), and requests that ANTS-B be added to the ActiveSet of theterminal managed by ANC.

Sequence (402)

When ANC receives the request (401) via ANTS-A, it prepares to deliverdownlink transmission data addressed to the terminal not only to ANTS-A,but also to ANTS-B (i.e., soft handoff is started), and instructsresource allocation of wireless channels in ANTS-B required for sendingand receiving to and from that terminal.

When the allocation is possible, the Active Set of the terminal isupdated, and this is notified to the terminal via ANTS-A (402). ANTS-Bthen starts to communicate with the terminal.

Sequence (403)

The terminal selects the base station with the best receiving conditionfrom among the base stations registered in the Active Set of theterminal, and specifies an base station ID in a DRCCover or DSC signalcontained in the uplink (terminal→base station) channel.

Sequence (404)

After the passage of a constant offset time, the base station specifiedby DRCCover or DSC starts downlink data transmission to the terminal.

Sequence (405)

The terminal monitors the received strength of the pilot signal fromeach base station included in the Active Set. When the received strengthfrom a base station (ANTS-A) falls below the threshold longer than afixed time, a Router Update message is transmitted, and it is requestedthat ANTS-A be deleted from the ActiveSet of the terminals managed byANC.

Sequence (406)

When ANC receives the request (405) via ANTS-A or ANTS-B, it terminatessoft handoff procedure, and after updating the Active Set, it instructsANTS-A to disconnect communication with the terminal. After receivingthis instruction, ANTS-A disconnects communication with the terminal.

Next, a soft handoff method expanded to multiple carriers for increasingthe maximum throughput, will be considered. As an example of a networkconfiguration, FIG. 1 shows an example of communication with the basestation wherein one terminal uses three carriers frequencies at the sametime. Downlink transmission data for the carrier frequencies f1-f3 ispassed from a PDSN (Packet Serving Data Node) 101 via the ANC 102(Access Node Controller) that is the control node of the base station,and is transmitted from the ANTS (Access Node

Transmission System)—A103 to an AT (Access Terminal) 105. Here, theaforesaid base station corresponds to ANTS and the terminal correspondsto AT. The AT (and the user who is using that terminal) 105 moves fromthe cell area of ANTS-A 103 to the cell area of ANTS-B104. Since radiowaves are attenuated depending on the propagation distance, the signalreceived from ANTS-A103 gradually becomes weaker. At the same time, softhandoff procedure occurs in each carrier, and finally, there is a shiftto communication between the three carriers and ANTS-B104 as shown inFIG. 2. Soft handoff is performed in a transitional situation wherein ATis present in the cell area of both ANTS between the aforesaid twostates.

The simplest way to shift from the state in FIG. 1 to the state in FIG.2 is a simultaneous soft handoff in all carriers altogether. However,reception characteristics of the terminal deteriorate if soft handoff isperformed for all carriers at the same time. In the worst case, there isa possibility that communication will be disconnected. This is because,if in multi-path condition, the propagation path has frequencyselectivity, meaning that the propagation path is different for carriersof different frequency. Therefore the pilot received strengthfluctuation at the terminal is different for every carrier (even ifANTS-B has a higher received strength than ANTS-A at two frequencies f1,f2, it does not necessarily mean that the ANTS-B is higher for f3 at thesame time). Further, in a wireless system, it may occur that thetransmission strength from the base station is different for eachcarrier, and that the frequency reuse pattern in an adjacent basestation is different. Due to above, when there is soft handoff for allcarriers at the same time, reception characteristics may deteriorate andcommunication may be disconnected.

Would the above mean that soft handoff should be performed independentlyfor each carrier? Actually, no. During hand off, wireless resources anddevice resources are consumed by multiple wireless stations. Forexample, if two base stations are in a handoff state for three carriersas shown in FIG. 3, control must be performed by AT105 for a total of 6carriers at most, so the battery life is reduced by the amount ofincreased processing which must be performed. Also, since wirelesschannel resources equivalent to a total of 6 carriers are used by oneterminal, if the soft handoff state persists for a long time, theresource will not be shared effectively among multiple users, so theusage efficiency of the whole system decreases.

Next, soft handoff in a second network configuration will be describedusing FIG. 8. In this configuration, ANC is installed in each AP, andAPs are connected by a CR (Router). Downlink circuit transmission dataat the carrier frequencies f1-f3 is passed from the PDSN (Packet DataServing Node) 801 via CR-A (Router), and is first transmitted from an AP(Access Point)—A803 to an AT (Access Terminal) 805. The AP 803 (804) hasfunctions corresponding to both ANC 102 and ANTS 103 in FIGS. 1-3. Inthis configuration, when soft handoff is performed, ANC in AP-A803 isthe main element which forwards data to AP-B 804 via CR-A 802 and CR-B806, and soft handoff is performed between AP-A 803 and AP-B 804 whichare contained in the Active Set of the terminal 805. In thisconfiguration also, if the soft handoff state persists for a long time,network resources are consumed due to forwarding of data between AP-A803 and AP-B 804, and it was therefore important to reduce the softhandoff procedure time.

Summarizing, it is therefore an object of the present invention, whichaims to resolve the above problems, to provide a terminal mobilityguarantee which offers sufficient performance in MC-CDMA, and which iseffective. The invention is applicable not only to MC-CDMA, but has thesame effect in a wireless communications system using a multiplexingtechnique such as OFDMA, OFDM or OFCDMA provided that the system is suchthat one terminal can communicate with a base station using multiplewireless resources, or soft handoff is performed between multiple basestations.

In the present invention, based on a receiving state notificationconcerning wireless resources from a terminal, soft handoff is forciblyterminated based on whether or not the data rate obtained for allresources on the network side satisfies a predetermined rate.

According to an embodiment of the present invention, a soft handoffperiod when one terminal communicates using multiple carriers at thesame time is shortened, sufficient received strength in the terminal ismaintained, and the mobility of the terminal is guaranteed, while on theother hand, a network forwarding load, terminal processing load andwireless resource allocation time can be suppressed to the minimum.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows how communication is performed during soft handoff whilesimultaneously communicating via three carriers in a first networkconfiguration;

FIG. 2 shows soft handoff for all carriers during simultaneouscommunication via three carriers in the first network configuration;

FIG. 3 illustrates how communication is performed during forced softhandoff termination from the network side during simultaneouscommunication via three carriers in the first network configurationaccording to the invention;

FIG. 4 is a flow chart of soft handoff in a prior art carrier system;

FIG. 5 is a flow chart showing a procedure in the first networkconfiguration according to a first embodiment of the invention;

FIG. 6 is a flowchart showing a procedure of soft handoff termination ina method according to the first embodiment of the invention;

FIG. 7 is a flow chart showing a procedure in the first networkconfiguration according to a third embodiment of the invention;

FIG. 8 illustrates how communication is performed during soft handoffduring simultaneous communication via three carriers in the secondnetwork configuration;

FIG. 9 is a flow chart showing a procedure in the second networkconfiguration according to the second embodiment of the invention;

FIG. 10 is a flow chart showing a procedure in the second networkconfiguration according to the fourth embodiment of the invention;

FIG. 11 is a schematic diagram of an ANC in the first networkconfiguration.

FIG. 12 is a schematic diagram of an ANTS in the first networkconfiguration; and

FIG. 13 is a schematic diagram of an AP in the second networkconfiguration.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1

A first embodiment of the present invention will now be describedreferring to FIG. 5. In this embodiment, a first example of a networkconfiguration is shown in FIG. 3. In this embodiment, the salient pointsare that soft handoff termination is periodically determined, andstability is maintained while redundant soft handoff is avoided. Toensure above points, soft handoff is terminated on the basis of thefollowing sequences.

Sequence (500)

It is assumed that soft handoff is performed at three frequencies (f1,f2, f3). The procedure for this will be described. Soft handoff at thesefrequencies may be performed at the same time, or soft handoff may beperformed one by one according to the propagation situation. The ActiveSet of each terminal is managed for each carriers. This is in agreementwith sequences (401)-(404) described in FIG. 4. The messages for f1-3 upto sequence (501) show that for carriers f1 and f2, since the receivingsignal quality from ANTS-B is better, data is received from ANTS-B, andfor carrier f3, since the receiving signal quality from ANTS-A isbetter, data is received from ANTS-A.

Sequence (501)

In the soft handoff state between multiple carriers, soft handofftermination judgments described later are performed periodically in ANC.

Sequence (502)

A case will now be considered where, in ANC, it is determined thatoverall communication quality is sufficient even if terminal AT performscommunication only with ANTS-B for carriers f1-f3. At this time, even ifthe reception quality of ANTS-A is still better for carrier f3 and anANTS-A disconnection request by a RouteUpdate message has not yet beenreceived from the terminal, ANC instructs ANTS-A to disconnect thecommunication with the terminal for all carriers f1-f3. ANTS-A whichreceived these instructions transmits a ConnectionClose message whichinstructs AT to terminate the communication, and AT which received thismessage disconnects communication with ANTS-A, after returning anAcknowledgement. ANC then deletes ANTS-A from the ActiveSet managedrespectively for each of the carriers f1-f3, and notifies the update tothe terminal via ANTS-B.

In ANC, in a predetermined period after soft handoff was forciblyterminated, no addition is made to the ActiveSet, even if a RouteUpdatemessage to ANTS-A is again sent from a terminal. Alternatively on theterminal side, in a predetermined period, even if the received strengthfrom ANTS-A is more than a threshold, a RouteUpdate message is nottransmitted. The latter method has the advantage that wireless resourcesare not consumed due to unnecessary exchange of messages, and a higherefficiency is obtained.

Soft handoff termination conditions as in the prior art were independentfor each carrier, and soft handoff termination conditions were notdetermined in view of multiple carriers. However, in one embodimentaccording to this invention, in ANC, if a soft handoff terminationjudgment is performed periodically and specific conditions are met, softhandoff is forcibly terminated from the network side regardless of thestate of each carrier, the soft handoff period is shortened, and animprovement in the operating efficiency of wireless resources andreduction of terminal battery consumption are thereby attained.

FIG. 6 shows an example of a flow chart of a soft handoff terminationjudgment in ANC in the aforesaid embodiment. As a precondition, it isassumed that send/receive data for all the carriers f1-f3 belongs to thesame data flow (hence, one data flow is actually distributed to, andtransmitted to and received from, three carriers). It is assumed alsothat ANC has information about the reception rate requested by theterminal with respect to the aforesaid data flow, or that it has ajudgment threshold corresponding to a preassumed request rate.

Step 600

A judgment about the request rate is made. If the data flow which is theobject of judgment is a QoS call which guarantees a predetermined QoS,the routine proceeds to a Step 603, and if it is anything other than aQoS call, the routine proceeds to a Step 604.

Step 601

When the data flow is determined to be a QoS call, it is assumed thatthe rate which should be guaranteed by QoS for the data flow is arequested sum total rate for all the carriers of this terminal.

Step 602

If it is anything other than a QoS call, the data flow is assumed to bea best effort call, and it is assumed that the minimum guaranteed ratepredetermined for a best effort call is the requested sum total rate forall the carriers of this terminal.

Step 603

ANC can acquire DRCCover or DSC notified from the terminal via the basestation ANTS-A or ANTS-B for each carrier, and the accompanying DRCRate(specification of the maximum data rate and communication format whichthe terminal can receive). DRCCover or DSC is uplink control informationwhich specifies a base station with the best receiving state among thebase stations registered in the ActiveSet of the terminal.

Based on the above information, ANC estimates the possible maximumthroughput rate which is the sum total for all carriers for the handofftarget base station (ANTS-B). An example for an effective estimationmethod is, to maintain DRCRate when DRCCover or DSC specifies thehandoff target base station (ANTS-B) for a specified time, and computean average estimated rate over a specified time. The characteristic ofthis invention is to estimate a total value for all carriers of thisterminal from the estimated rate for each carrier. Various methods canbe used in estimation of the above, depending on the purpose and withinthe scope of the invention. It is then determined whether or not theestimated rate which can be received which is the sum total for allcarriers, exceeds the requested total rate.

Step 604

Even if, as a result of Step 603, the requested total rate isinstantaneously exceeded, it may also fall below the requested totalrate due to a change in the propagation path. However, once soft handoffis terminated, it is necessary to resume communication with ANTS-Aimmediately and to exchange control messages between the base stationand terminal repeatedly to return to the soft handoff state (thisoperation is called “disconnection return”), and a long processing timeis therefore required. The reception quality in the terminal not onlydeteriorates, but the network transmission load and terminal processingload increase, and the utilization efficiency of wireless resourcesfalls. Hence, after verifying that the requested sum total rate can besatisfied with some degree of certainty only by communication withANTS-B, it is judged that sufficient reception quality can already beobtained even if transmission from the origin of the handoff (ANTS-A) isstopped. The method of estimating the certainty may be a verificationthat the judgment result of 603 holds continuously a predeterminednumber of times or more, or by averaging the judgment result of 603 inthe time direction, and verifying that it holds a predetermined numberof times or more within a fixed time.

Step 605

ANTS-A which is the origin of the handoff is then instructed to performsoft handoff termination (i.e., communication disconnection).

In ANC, a downlink scheduler operates. The scheduler changes the methodof channel allocation according to whether transmission for thecorresponding terminal guarantees QoS. Therefore, ANC knows informationabout QoS beforehand and soft handoff termination conditions are alsojudged using the information.

In the above, the rate guaranteed for a best effort call in Step 602 maybe changed according to the wireless situation or terminal priority.

For example, the guaranteed rate may be changed depending on the deviceresources of the base station. Since a high user rate for the terminalcan be ensured by increasing the guarantee rate when there aresufficient device resources, the serviceability of the system improves.The guarantee rate may be changed based on interference powerinformation measured in the base station. When interference power islarge, a shortage of wireless resources can be predicted. The guaranteerate is lowered in such a case, and the system is modified so that moreterminals can be connected.

If it is a terminal to which priority should be given, the guaranteerate can also be set higher. In this way, serviceability can be providedaccording to, for example, a fee system.

In Step 601, the sum total of the possible throughput rate for ANTS-Awhich is the origin of soft handoff, is compared with a requested sumtotal rate, and soft handoff forced termination of the soft handofftarget ANTS-B (added to the Active Set later) may be determined.

In the case of the first embodiment, to perform soft handoff terminationfor all carriers of the terminal, the Active Set can be managed for eachcarrier, or one Active Set can be managed globally for one terminalwithout managing the Active Sets for each carrier. Further, in the firstembodiment and other embodiments, the case was described where therewere three carriers, but the invention may also be applied to multiplecarriers without limit.

Embodiment 2

FIG. 9 shows a flow chart when applying the first embodiment in theaforesaid second network configuration. In this embodiment, as in thefirst embodiment, a soft handoff termination judgment is madeperiodically, and a prolonged soft handoff state is avoided whilemaintaining stability.

Hence, soft handoff is terminated based on the following sequences.

Sequence (900)

It is assumed that there is a soft handoff state at three frequencies(f1, f2, f3). The procedure for this will now be described. These maybein a soft handoff state simultaneously, or may be in a soft handoffstate one by one according to the transmission state. This is equivalentto the sequences (401)-(404) described in FIG. 4. The difference is thatsince ANC in FIG. 4 is divided into multiple parts, data is sent fromPCF/PDSN to ANC-A which is the origin of soft handoff until soft handoffis completed, and when soft handoff is completed, the soft handofftarget is changed to ANC-B. During soft handoff, when the terminalrequests data to be transmitted to the soft handoff target ANTS-B, datais forwarded from ANC-A to ANC-B, and then data is transmitted fromANC-B to the terminal via ANTS-B. The reason for adopting this format isto avoid generating a “disconnection return” between ANC-A and ANC-B.

Sequence (902)

An ANC-A901 in AP-A which is the main element judges whether or not softhandoff termination is feasible.

Sequence (904)

When it is judged to forcibly terminate soft handoff for AP-A, a handoffrequest message which requires taking over data flow control to thisterminal is transmitted from ANC-A to ANC-B 903 in AP-B and PCF/PDSN.

ANC-B which received the handoff request receives data from PCF/PDSN,and makes preparations to forward the data to ANTS-B. PCF/PDSN alsomakes preparations to route the data already transmitted to AP-A, toAP-B.

Sequence (906)

If an ACK905 which notifies acceptance of a handoff request is returnedby ANC-B, ANC-A instructs ANTS-A to disconnect communication with theterminal for all the carriers f1-f3. The operations of ANTS-A and ATwhich received the disconnection instruction are identical to that ofthe first embodiment.

Embodiment 3

A third embodiment will now be described referring to FIG. 7. In thisembodiment, when a RouteUpdate message for soft handoff termination isreceived from the terminal for one carrier among multiple carriers(equivalent to sequence 405), the same soft handoff termination judgmentis made as in the case of the first embodiment (701). For example, asshown by 500 of FIG. 5, when there is a soft handoff state for all thecarriers f1-f3 and an instruction to terminate soft handoff for f1 isnotified from the terminal side, it is instructed to terminate softhandoff also for the carriers f2, f3 which are still in the soft handoffstate.

Also in this case, by shortening the soft handoff period, operatingefficiency of wireless resources can be increased and terminal batteryconsumption can be reduced. As compared with the case of the firstembodiment which periodically judges the feasibility of disconnection ofANTS-A continuously from soft handoff Start, the risk of “disconnectionreturn” occurring can be suppressed low by waiting until soft handoff isterminated for one carrier. Since the judgment period is also shortened,the processing load of ANC is also suppressed.

Embodiment 4

FIG. 10 is a flow chart showing a case where, in the aforesaid secondnetwork configuration, a software handoff termination decisionpreparation is made in the same way as in the third embodiment. As inFIG. 9, an ANC-A1001 of AP-A is the main element which judges thefeasibility of soft handoff termination for all the carriers of theterminal based on a notification of soft handoff termination for any onecarrier received from the terminal (1002). A handoff request messagewhich requires taking over data flow control to this terminal istransmitted to an ANC-B1003 in AP-and PCF/PDSN (1004). When an ACK1005which notifies acceptance of the handoff request from ANC-B is returned,ANC-A instructs ANTS-A to disconnect communication with the terminal forall carriers. The operations of ANTS-A and AT which received thecommunication disconnection instruction are identical to those of thethird embodiment.

Embodiment 5

In the first embodiment, soft handoff termination to avoid soft handoffusing multiple carriers was described, but even if there is atermination from the soft handoff state, a new RouteUpdate message isissued by the terminal immediately due to the received strength, andthere may be a return to the soft handoff state with multiple carrierswhich would offset the effect of the invention. Therefore, somemodification is required also of the part shown by 500 of FIG. 5. Thefollowing two methods constitute the fifth embodiment of this patent.

Firstly, control of the RouteUpdate message may be mentioned.

When the terminal is in the soft handoff state, according to the numberof carriers to be connected, a threshold in a pilot reception powerjudgment method for transmitting a RouteUpdate message with a newcarrier is changed. For example, when it is not in the present softhandoff state and the pilot received power of a new base station exceedsa threshold 1 in the first carrier, soft handoff in the first carrier isstarted. Next, when the pilot received power of the new base stationexceeds a threshold 2 in the second carrier, soft handoff in the secondcarrier is started. Next, when the pilot received power of the new basestation exceeds threshold 3 in the third carrier, soft handoff in thethird carrier is started. The relation between the thresholds at thistime is set to be threshold 1<threshold 2<threshold 3. Since suitablethreshold values cannot be estimated by the terminal alone, a messagewhich specifies the aforesaid threshold 1, threshold 2, and threshold 3is broadcast from the base station. Hence, the probability of softhandoff occurring in multiple carriers simultaneously can be controlledby the threshold operation. This solves the problem.

In this embodiment, changing the above-mentioned threshold by QoS orbest effort is also within the scope of the invention. A minimum rate isguaranteed by setting the best effort thresholds to have the relationthreshold 1<<threshold 2<<threshold 3 (increasing the difference betweenthe thresholds) and for QoS calls, the QoS guarantee is made easier touse by setting threshold 1<threshold 2<threshold 3 (decreasing thedifference between the thresholds).

Secondly, there is the method of rejecting the Route Update message. Inthis embodiment, a Route Update message is often emitted by theterminal, and conversely, the hand off target ANTS is rejected. ANTStemporarily stores the ID of a terminal which performed the softhandoff, and makes connection with a terminal which requires a re-softhandoff within a definite period of time. Due to this, a soft handoffwith hysteresis can be performed, and the problem can be resolved forexample by combining this with the first embodiment.

Embodiment 6

The composition of ANC in the first network example will now bedescribed using FIG. 11. The ANC has a network interface part 1101 forperforming transmission and reception of control messages orcommunication data exchanged with PCF/PDSN, network interface part 1102for performing transmission and reception of communication dataexchanged with each ANTS, a control part 1103, and a data processingpart 1104 which performs processing of communication data. The controlpart 1103 performs management of the Active Set and performs updating ofActive Set information of the terminal which corresponds to reception ofa control message during soft handoff start and termination.Transmission/reception control of control messages required for softhandoff start and termination control is also performed, including thesoft handoff termination judgment described in FIG. 6. Transmissioncontrol for distributing terminal communication data to ANTS is alsoperformed during, before and after soft handoff.

Embodiment 7

The construction of an ANTS in the first network configuration examplewill now be described referring to FIG. 12. ANTS has a network interfacepart 1201 for sending and receiving control messages and communicationdata to and from ANC, a wireless part 1202 for sending and receivingcontrol messages and communication data to and from AT, a control part1203, and a data processing part 1204 which performs processing ofcommunication data. The control part 1203 has a message interface forcommunicating the possible terminal reception rate for each carrierwhich is required for the soft handoff termination judgment describedbased on FIG. 6, to ANC.

Embodiment 8

AP in the second example of a network configuration has the function ofthe ANC of FIG. 11 and ANTS of FIG. 12 in one case. Specifically, asshown in FIG. 13, it has a network interface part 1301 forsending/receiving control messages and communication data to and fromCR, wireless part 1302 for sending/receiving control messages andcommunication data to and from AT, ANC control part 1303 which has thesame functions as the ANC control part and data processing part of FIG.11, ANC data processing part 1304, ANTS control part 1305 which has thesame functions as the ANTS control part and data processing part of FIG.12, and ANTS data processing part 1306. The operating functions of eachof the parts 1303-1306 are essentially identical to those of thecorresponding parts in FIGS. 11 and 12. However, if this AP is theorigin of the hand off, the ANC performs control for forwardingcommunication data addressed to a terminal to the ANC of the target APvia CR. When this AP is the handoff target, control which receivesforwarding of communication data addressed to the terminal from the ANCof the AP which is the origin of the hand off via CR, is performed. TheANC control part also performs processing of control messages forhandoff between AP.

1. A control node connected between multiple base stations which performcommunication between terminals using multiple carriers, these multiplebase stations and a network, soft handoff of said terminal beingperformed among these multiple base stations, wherein said node has: afirst network interface part that performs transmission and reception ofcommunication data of said terminal with said network; a second networkinterface part that performs transmission and reception of communicationdata of said terminal between first and second base stations; and acontrol part, wherein, when said terminal is in a soft handoff statebetween said first and second base stations, said second networkinterface part receives communication quality information about multiplecarriers between this first or second base station and this terminal viasaid first or second base station, and wherein, the control partdetermines termination of a soft handoff of at least a second carrierbased on the received communication quality information about saidterminal from said first or second base station at least a firstcarrier, and notifies a network side soft handoff termination messagewhich instructs the termination of a soft handoff of at least a secondcarrier to said terminal from said first or second base station.
 2. Thecontrol node according to claim 1, wherein said communication qualityinformation is information on a data rate obtained by any one of thebase stations in each carrier, and wherein, when a data rate for all thecarriers of the corresponding terminal obtained from said first orsecond base station exceeds a predetermined request rate, said controlpart makes a judgment to terminate soft handoff of all the carriers forsaid second or first base station.
 3. The control node according toclaim 2, wherein said predetermined request rate is a QoS rate of thisterminal or a best effort guarantee rate determined by each basestation.
 4. The control node according to claim 1, wherein when aterminal side soft handoff termination message which notifiestermination of soft handoff for said first base station in said firstcarrier is received from said terminal, said control part makes ajudgment to terminate soft handoff for said first base station also insaid second carrier.
 5. The control node according to claim 1, whereinsaid control part, after notifying said network side soft handofftermination message for said first or second base station to saidterminal, refuses a request which adds said first or second base stationfrom this terminal to the Active Set according to predeterminedconditions.
 6. A base station in a wireless communications system havingmultiple base stations connected to a network which performcommunication with a terminal using multiple carriers, soft handoff ofsaid terminal being performed among these multiple base stations, saidbase station comprising: a network interface part which performstransmission and reception of communication data of said terminal withthe network and with other base stations; a wireless part which performstransmission and reception of communication data between said basestations; and a control part, wherein when said terminal is in a softhandoff state between this base station and other base stations, andwhen this base station is the origin of the base station handoff, saidnetwork interface part forwards communication data addressed to aterminal received from the network to said second base station, andwherein said control part notifies a network side soft handofftermination message which instructs termination of soft handoff of atleast a second carrier to be determined based on the receivedcommunication quality information due to said base station or said otherbase stations for at least a first carrier, to said terminal from saidfirst or second base station.
 7. The base station according to claim 6,wherein said communication quality information is information about adata rate obtained by any one of the base stations in each carrier, andwherein when a data rate for all the carriers of the terminal concernedobtained from this first or second base station exceeds a predeterminedrequest rate, said control part makes a judgment to terminate softhandoff of said second or first base station for all the carriers. 8.The base station according to claim 7, wherein said predeterminedrequest rate is a QoS rate of this terminal, or a best effort guaranteerate determined by this base station.